doc: document the new Cgo EGLConfig special case
doc: document the new Cgo EGLConfig special case

Change-Id: I7ae5eaa974b85eac421a0b1f79cb734a0fe44e72
Reviewed-on: https://go-review.googlesource.com/c/go/+/235818
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

akutz/go,akutz/go,cloudflare/go,akutz/go,akutz/go,akutz/go,nawawi/go,nawawi/go,nawawi/go,nawawi/go,CAFxX/go,akutz/go,nawawi/go,golang/go,cloudflare/go,cloudflare/go,cloudflare/go,CAFxX/go,CAFxX/go,akutz/go,CAFxX/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,golang/go,nawawi/go,cloudflare/go,cloudflare/go,CAFxX/go,golang/go,CAFxX/go,golang/go,golang/go,CAFxX/go,akutz/go,golang/go,golang/go,nawawi/go,cloudflare/go